Sensitized silver halide systems with activated nonlabile selenium compounds



United States Patent 3,442 653 SENSITIZED SILVER HALIDE SYSTEMS WITHACTIVATED NONLABILE SELENI- UM COMPOUNDS Joseph S. Dunn, Rochester,N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporationof New Jersey No Drawing. Continuation-impart of application Ser. No.468,972, July 1, 1965. This application Mar. 29, 1968, Ser. No. 717,396

Int. Cl. G03c 1/50, N

US. Cl. 96-108 Claims ABSTRACT OF THE DISCLOSURE Sensitizingphotographic systems such as a silver halide emulsion with a noble metaland labile selenium formed in situ by activating a non-labile seleniumcompound. Specific activation methods include the use of reducingagents.

This application is a continuation-in-part of my copending applicationSer. No. 606,587 filed Jan. 3, 1967, now abandoned, which is acontinuation-in-part of my application Ser. No. 468,972 filed July 1,1965, now US. Patent No. 3,297,446 which in turn was acontinuationin-part of Ser. No. 343,465 filed Feb. 10, 1964, nowabandoned.

This invention relates to photography. In one aspect, this inventionrelates to processes of sensitizing photographic systems.

In my earlier-filed application Ser. No. 468,972, now US. Patent3,297,446, I found that a sensitizer combination of a noble metal andlabile selenium produced a synergistic effect in photographic systems.There are many readily available selenium compounds which are notlabile, however, and it would be desirable to employ these compounds ina sensitizing process. The invention provides a way for employing thesecompounds in such a sensitizing process.

It is an object of this invention to provide a process for sensitizingphotographic systems with a noble metal and labile selenium wherein anon-labile selenium compound is employed in the process.

Another object of this invention is to provide a process for sensitizingphotographic silver halide emulsions with a noble metal and labileselenium wherein a non-labile selenium compound is employed in theprocess.

Still another object of this invention is to provide a process forsensitizing photographic systems and more particularly silver halideemulsions with gold and labile selenium wherein a non-labile seleniumcompound is employed in the process.

Yet still another object of the invention is to provide a sensitizingprocess for photographic systems which can be easily controlled.

Other objects will become apparent hereinafter.

These and other objects of the invention are accomplished by sensitizingphotographic systems and more particularly silver halide emulsions witha noble metal and labile selenium which is formed in situ by activatinga non-labile selenium compound. It was previously thought Patented May6, 1969 whenever desired by activating the non-labile selenium compoundat that time. The degree of sensitization can also be controlled byvarying the intensity of activation. A predetermined sensitivity of aphotographic system can thus be obtained with the sensitizing process ofthis invention.

Any method for activating non-labile selenium compounds can be used inthis invention so long as it renders the selenium compounds labile. Apreferred way of activating non-labile selenium compounds to make themlabile is by employing reducing agents. Other methods for activatingnon-labile selenium compounds to make them labile are disclosed andclaimed in copending application Ser. Nos. 606,586 and 606,588 bothentitled sensitizing Photographic Systems of my co-worker Mc- Veighfiled concurrently herewith.

The term labile has a meaning well understood by those skilled in theart of photography and is defined in my earlier-filed application Ser.No. 468,972, filed July 1, 1965 now US. Patent 3,297,446, as being amaterial which yields a silver selenide that is insoluble in water atroom temperature (20 C.) upon addition to an aqueous silver nitratesolution. Likewise, the term non-labile as used herein in describingselenium compounds has a meaning well understood by those skilled in theart of photography, i.e., a material which does not yield a .silverselenide that is insoluble in water at room temperature (20 C.) uponaddition to an aqueous silver nitrate solution. For example, potassiumselenocyanate and selenous acid are nonlabile selenium compounds sincesilver selenide does notprecipitate when these compounds are added to anaqueous silver nitrate solution.

Non-labile selenium compounds which can be used in this inventioninclude, for example, potassium selenocyanate, selenous acid, inorganicisoselenocyanate complexes, etc.

The concentration of the non-labile selenium compound which is activatedto form labile selenium in situ can be varied considerably dependingupon the particular nonlabile selenium compound employed, the nature ofthe photographic system, the amount and chemical nature of the noblemetal sensitizer, etc. In silver halide systems, for example, I havefound that useful results can be obtained using amounts as small as 0.05mg. of non-labile selenium compound per mole of silver halide althoughconsiderably larger amounts can also be employed, such as 5.0 mg. ormore per mole of silver halide.

The noble metal sensitizers useful in my invention include thewell-known gold sensitizers and other noble metals such as palladium,platinum and any of those disclosed in Smith et al., US. Patent No.2,448,060, issued Aug. 31, 1948. Typical suitable gold sensitizers aredescribed in Waller et al., US. Patent No. 2,399,083, issued Apr. 23,1946, and Damschroder et al., US. Patent 2,642,- 361, issued June 16,1953.

Illustrative addenda suitable for furnishing the noble metal moiety inthe sensitizer combinations of the invention include:

gold chloride,

potassium aurate,

potassium auriaurite,

potassium auricyanide,

potassium aurithiocyanate,

gold sulfide,

gold selenide,

gold iodide,

potassium chloroaurate, ethylenediamine-bis-gold chloride, I ammoniumchloroplatinite, i.e. (NH PtCl ammonium chloropalladate, i.e. (NHQ PdCland 3 organic gold sensitizers having the formulas:

C-SAu II. s

G-SAu III:

N-C H o=orr-on=o (I 2 5 SAI1 N S 31115 IV: (H)

\ N-onn C=C 'SAu /CCH; 03H; A1101 VI. /S\ g2 g2 C-CH=CHN 011, c-C N\ H22 C AuClt VII.

OH N N N CzHt AuCh CgHs AuCll The concentration of noble metalsensitizer useful in my invention can be any amount suitable for theintended purpose. I have found, for example, that amounts varying fromabout 0.1 to about 5.0 mg. of gold sensitizer per mole of silver halideare quite satisfactory.

In Example 8 of my earlier-filed application Ser. No. 468,972, U.S.Patent 3,297,446, I disclosed that compounds containing a selenium atomwhich is not labile do not provide the very high increase in speeddescribed therein for combinations including nabile selenium'compounds.I have found, however, that non-labile selenium compounds can beactivated in accordance with the instant invention to convert theselenium to a labile state. After activation, these compounds, incombination with noble metals, perform in the same manner as the labileselenium compounds in my previous case and act as a synergisticsensitizer combination to give the very high photograhic speed disclosedin said previous case.

As was previously indicated, a preferred method of the invention foractivating non-labile selenium compounds is by employing a reducingagent. Any reducing. agent can be employed which is effective for theintended purpose. Among reducing agents which can be used arebenzothiazolium salts such as benzothiazole methiodide, benzothiazolemethbromide, 2 -hydroxy-methyl-benzothiazole ethyliodide, 2hydroxymethyl-benzothiazole methiodide, etc.; mercaptans such asZ-mercaptobenzoic acid, thiolactic acid, Z-mercapto benzothiazole, etc.;disulfides such as diphenyl disulfidie; triphenylphosphine; stannouschloride; benzothiazoline compounds such as 3-methyl-benzothiazoline,2-methyl-3-methyl-benzothiazoline, 2,2-dimethyl-3-methyl-benzothiazoline, etc.; alkali metal sulfites such as potassiumsulfite, sodium sulfite, etc.

The reducing agent can be added directly to the sensitizer mixture andreacted with the non-labile selenium compound to form labile selenium insitu or it can be added to the photographic system, e.g., a silverhalide emulsion, after the sensitizers are added to form labile seleniumin situ. If desired, the reducing agent can also be previouslyincorporated into the photographic system, such as in the gelatin of asilver halide emulsion. The concentration of the reducing agent can, ofcourse, be considerably varied depending upon the particular non-labileselenium compound employed, the concentration of the non-labile seleniumcompound, the nature of the photographic system, etc. Preferably, theconcentration of the reducing agent is in stoichiometric excess of thenon-labile selenium compound being reduced. Suitable concentrationsinclude, e.g., 1 to about 50 mg. per silver mole.

It has been found that particularly useful results are obtained when thesensitizer mixture used in the .sensitizing process of the inventioncontains a watersoluble thiocyanate compound. Typical thiocyanatesinclude sodium thiocyanate, potassium thiocyanate, ammonium thiocyanate,etc. The amount of thiocyanate compound used can be varied dependingupon the particular system being sensitized, relative amounts ofscnsitizers employed, etc.

The sensitizing addenda, before or after activation according to myinvention, can be added in a variety of ways to photographic systems andat various stages in the preparation of such. In general, with respectto silver halide emulsions, such addenda can be added with usefuleffects at the completion of the Ostwald ripening and prior to one ormore of the final digestion operations. The sensitizing addenda arepreferably added to silver halide emulsions after the silver halidegrains are substantially in their final size and shape. The addenda canbe added in the form of their aqueous solutions, where they are solublein water, or in an innocuous organic solvent where the sensitizer doesnot have suflicientsolubility in water to be used in the form of anaqueous solution. Particularly useful organic solvents include ethanol,methanol, pyridine, acetone, dioxane, etc. Organic solvents which have arather high degree of polarity are preferred. Where it is desired to addthe sensitizing addenda in some other form than a solution, thisprocedure is also possible, especially where the sensitizer is availablein the form of a colloidal suspension. In some cases, it is possible toadd the sensitizers suspended in an organic solvent which forms verysmall suspended particles in the photographic emulsion similar to thetype of colloidal particle produced in preparing coupler dispersions.Dispersing media useful for this purpose include tricresyl phosphate,dibutyl phthalate, triphenyl phosphate, etc.

Vacuum deposited photographic systems substantially free of conventionalvehicles, binders or dispersing agents can also be sensitized inaccordance with the invention by incorporating the sensitizers, beforeor after activation, in a coating or layer contiguous to the vacuumdeposited light-sensitive material. Suitable vacuum deposited silverhalide systems that can be sensitized in accordance with the inventionare disclosed in Rasch et a1. application U.S. Ser. No. 415,596 filedDec. 3, 1964; Rees application U.S. Ser. No. 421,725 filed Dec. 28, 1964now US. Patent 3,384,490; and Belgian Patent 639,020.

The silver halide emulsion of a photographic element which can besensitized according to this invention can contain conventional addendasuch as gelatin plasticizers, coating aids, antifoggants such as theazaindines and hardeners such as aldehyde hardeners, e.g., formaldehyde,mucochloric acid, glutaral'dehyde bis(sodium bisu-lfite), ma leicdialdehyde, aziridines, dioxane derivatives and oxypolysaccharides. Theaddenda may be added to the emulsion before or after sensitizing dyes,if any, are used. Sensitizing dyes useful in sensitizing such emulsionsare described, for example, in US. Patents 2,526,632 and 2,503,776.Spectral sensitizers which can be used are the cyanines, merocyanines,complex (trinuclear) cyanines, complex (trinuclear) merocyanines,styryls and hemicyanines. Developing agents can also be incorporatedinto the silver halide emulsion if desired or can be contained in aseparate underlayer. Various silver salts may be used as the sensitivesalt such as silver bromide, silver iodide, silver chloride, or mixedsilver halides such as silver chlorobromide or silver bromoiodide.

The silver halide emulsion layer of a photographic element which can besensitized according to the instant invention can contain any of thehydrophilic waterpermeable binding materials suitable for this purpose.Suitable materials include gelatin, colloidal albumin, polyvinylcompounds, cellulose derivatives, acrylamide polymers, etc. Mixtures ofthese binding agents can also be used. The binding agents for theemulsion layer of the photographic element can also contain dispersedpolymerized vinyl compounds. Such compounds are disclosed, for example,in US. Patents 3,142,568; 3,193,386; 3,062,674; and 3,220,844, andinclude the water-insoluble polymers of alkyl acrylates andmethacrylates acrylic acid, sulfoalkyl acrylates or methacrylates andthe like.

The silver halide emulsion of a photographic element which can besensitized according to the instant invention may be coated on a widevariety of supports. Typical supports are cellulose nitrate film,cellulose ester film, polyvinyl acetal 'film, polystyrene film,poly(ethylene terephthalate) film and related films or resinousmaterials as well as glass, paper, metal and the like. Supports such aspaper which are coated wtih a-olefin polymers, particularly polymers ofwolefins containing two or more carbon atoms, as exemplified bypolyethylene, polypropylene, ethylene butene copolymers and the like canalso be employed.

I have found that the speed of photographic emulsions sensitizedaccording to the invention can be further increased by including in theemulsions a variety of hydrophilic colloids, such as carboxymethylprotein of the type described in US. Patent 3,011,890, issued Dec. 5,Canadian Patent 635,206.

Photographic emulsions sensitized according to the invention can containspeed increasing compounds such as quaternary ammonium compounds,polyethylene glycols or thioethers. Frequently, useful effects can beobtained by adding the aforementioned speed increasing compounds to thephotographic developer solutions instead of, or in addition to, thephotographic emulsions.

The sensitizing process of the invention can be used for various kindsof photographic systems. In addition to being useful in X-ray and othernonoptically sensitized systems, they can also be used inorthochromatic, panchromatic, and infrared sensitive systems. Thesensitizing addenda can be added to photographic systems before or afterany sensitizing dyes which are used.

The sensitizing process of the invention can be used in emulsionsintended for color photography, for example, emulsions containingcolor-forming couplers or emulsions to be developed by solutionscontaining couplers or other color-generating materials, emulsions ofthe mixed-packet type, such as described in Godowsky US. Patent2,698,794 issued J an. 4, 1955; in silver dye-bleach systems; andemulsions of the mixed-grain type, such as described in Carroll andHanson US. Patent 2,592,243, issued Apr. 8, 1952.

The sensitizing process of the invention can be utilized to sensitizeany photographic system that can be sensitized with noble metals. Theinvention thus has utility, not only for silver halide photographicsystems, but also for other light-sensitive systems such as otherlight-sensitive silver salts, thallous halides, cuprous halides, leadhalides and related light-sensitive heavy metal salts.

Photographic elements which have been sensitized according to theprocess of the instant invention may be stabilized with labile sulfurcompounds in accordance with application Ser. No. 486,235 of McVeighfiled Sept. 9, 1965, now US. Patent 3,297,447. These labile sulfurcompounds provide a particularly efficacious means of controlling fogwithout deleteriously affecting the speed of the stabilized photographicsystem. Particularly useful labile sulfur compounds include thewater-soluble thiosulfates such as alkali metal thiosulfates includingsodium and potassium thiosulfates, as well as ammonium thiosulfate;thioureas such as thiourea, allylisothiourea, diacetyl thiourea;thiosemicarbazide; thiocarbamates such as isopropylthiocarbamate; etc.

The amount of labile sulfur compound used to stabilize photographicsystems sensitized by the process of this invention can varyconsiderably depending upon the particular sensitized photographicsystem employed, finishing conditions, including temperature and time ofdigestion and ripening, etc. In silver halide photographic systems,particularly useful results have been obtained at concentrations ofabout 0.1 to 10 mg. per mole of silver halide. Larger or smallerquantities can be employed without adversely affecting the sensitometricproperties of the photographic system. The labile sulfur compounds areefficaciously added to be present during the chemical sensitization ofthe photographic system.

The following examples will illustrate the invention but are not to beconstrued to limit it in any way.

EMMPLE 1 Activation by reducing agents A medium grain silver bromoiodideemulsion containing 3.4 mole percent iodide is prepared. A first portionof the emulsion is chemically sensitized by the addition of 2 mg. ofpotassium chloroaurate per silver mole, mg. of potassium thiocyanate persilver mole and 1.6 mfi. of potassium selenocyanate per silver mole. Theemulsion is then heated for 40 minutes at 65 C.

A second portion of the emulsion is sensitized in the same manner as thefirst portion but with'the addition of 10.1 mg. of benzothiazolemethiodide per silver mole and heating for 9 minutes at 65 C.

A third portion of the emulsion is sensitized in the same manner as thefirst portion except for the addition of 8.2 mg. of benzothiazolemethbromide per silver mole and heating for 9 minutes at 65 C.

A fourth portion of the emulsion is sensitized in the same manner as thefirst portion except for the addition 8 per silver mole.The emulsion isthen heated for 30 minutes at 60 C.

A second portion of the emulsion is sensitized in the same manner as thefirst portion except for the addition of 2.8 mg. of triphenylphosphineper silver mole and of 11.7 mg. of 2-hydroxymethy1benzothiazoleethyliodide 5 heating for 6 minutes at 60 C. per silver mole and heatingfor 12 minutes at 65 C. A third portion of the emulsion is sensitized inthe These emulsions are then coated on a cellulose acesame manner as thefirst portion except for the addition tate support at a coverage of 540mg. of silver per square of 10.1 mg. of benzothiazole methiodide persilver mole foot. The coatings are then exposed on an intensity scaleand heating for 20 minutes at 60 C. sensitometer, processed for 5minutes in Kodak Developer These emulsions are then coated and processedin the DK-SO, fixed, washed and dried. same manner as in Example 1 withthe following results:

The following results are obtained:

Relative R01 ative 15 Portion Reducing agent speed Fog Portion Reducingagent speed g First None 10 Q 02 Second... Triphenylphosphine 100 0.06ggi fothiazole methiodide Benzothlazole methlodldo 100 ThirdBenzothiazole methbromi 240 0.21 Fourth 2-hydroxymethyl-benzothiazole204 0.27

methiodide. Th1s example shows that reducing agents convert a non-labileselenium compound into a labile form WhlCh This example shows thatreducing agents activate pois a efl tiv sensitizer, tassiumselenocyanate to make it labile with an increase EXAMPLE 4 in speed ofup to 140%. E 1 H M 1 t th quiva ence o a 1 e se enium sens1 12ers W1EXAMPLE 2 activated non-labile selenium compounds Actlvatlon by otherreducmg agents A first portion of the emulsion of Example 1 is chemi- Afirst portion of the emulsion of Example 1 is chemcally sensitized with2 mg. of potassium chloroaurate per ically sensitized with 2 mg. ofpotassium chloroaurate silver mole, 100 mg. of potassium thiocyanate persilver per silver mole, 100 mg. of potassium thiocyanate per mole and0.8 mg. of N,N-dimethylselenourea per silver silver mole and 1.6 mg. ofpotassium selenocyanate per mole. The sensitized emulsion is then heatedfor 15 minsilver mole. The sensitized emulsion is then heated for utesat 65 C. 40 minutes at 65 C. A second portion of this emulsion ischemically sensi- A second portion of the emulsion is chemicallysensitized with 4 mg. of potassium chloroaurate per silver tized with 4mg. of potassium chloroaurate per silver mole, 100 mg. of potassiumthiocyanate per silver mole, mole, 100 mg. of potassium thiocyanate persilver mole, 1.6 mg. of potassium selenocyanate per silver mole and 1.6mg. of potassium selenocyanate per silver mole and 20.2 mg. ofbenzothiazole methiodide per silver mole. 20.2 mg. of benzothiazolemethiodide per silver mole. This portion of the emulsion is also heatedfor 15 minutes This portion is then heated for 15 minutes at 65 C. at 65C.

A third portion of the emulsion is sensitized in the 40 These emulsionsare then coated and processed in the same manner as the second portionexcept that the benzosame manner as in Example 1 with the followingresults:

Relative Portion sensitizers Reducing agent speed Fog First Potassiumchloroaurate-N,N- None 1,000 0.21

dimethylselenourea. Second--- Potassium ehloroaurate-Po- Benzothiazolemethi- 970 0.17

tassium selenocyanate. odide.

Relative Portlon Reducing agent speed Fog First None 100 0.03 Second.Benzothiazole methiodide.. 302 0. 17 Third 2-mercaptobenzoic acid 2890.20

EXAMPLE 3 Activation by reducing agents in the absence of a noble metalA first portion of the emulsion of Example 1 is chemically sensitizedwith 100 mg. of potassium thiocyanate per silver mole and 1.6 mg. ofpotassium selenocyanate This example shows that non-labile compoundswhich are activated by reducing agents are equivalent in theirsensitizing action to labile selenium compounds.

EXAMPLE 5 Equivalence of labile selenium sensitizers with activatednon-labile selenium compounds A first portion of the emulsion of Example1 is chemically sensitized with mg. of potassium thiocyanate per silvermole and 0.8 mg. of N,N-dimethylselenourea per silver mole. Thisemulsion is then heated for 9 minutes at 60 C.

A second portion of this emulsion is sensitized with 100 mg. ofpotassium thiocyanate per silver mole, 1.6 mg. of potassiumselenocyanate per silver mole and 1.4 mg. of triphenylphosphine persilver mole. This emulsion is then heated for 6 minutes at 60 C.

These emulsions are then coated and processed in the same manner as inExample 1 with the following results:

Portion Sensitizer Relative 9 EXAMPLE 6 Synergistic effect of reducingagent with non-labile selenium compound A first portion of the emulsionof Example 1 is sensitized with 100 mg. of potassium thiocyanate persilver mole and 2.8 mg. of triphenylphosphine per silver mole. Thisemulsion is then heated for 30 minutes at 60 C.

A second portion of the emulsion is sensitized with 100 mg. of potassiumthiocyanate per silver mole and 1.6 mg. of potassium selenocyanate persilver mole and then heated for 30 minutes at 60 C.

A third portion of the emulsion is sensitized in the same manner as thefirst portion but the addition of 1.6 mg. of potassium selenocyanate persilver mole and heating for 6 minutes at 60 C.

dimethyl selenourea is disclosed as being labile in my earlier filedapplication Ser. No. 468,972, filed July 1, 1965, now US. Patent3,297,446).

EXAMPLE 8 Comparison of activated non-labile selenium compounds Withconventional sensitizers Relative Portion Sensitizer Reducing agentspeed Gamma Fog First Sodium thiosulfate-potassium chloro- None 750 0.93 0, 14

aura e.

Second. Selenous acid potassium chloroaurate. Sodium sulfite. 1,000 1.03 0.14

These emulsions are then coated and processed in the same manner as inExample 1 with the following results:

This example illustrates the synergistic eifect which is obtained when areducing agent is combined with a nonlabile selenium compound. Anincrease in speed of 1000% is obtained.

This example shows that gold and non-labile selenium compounds whichhave been made labile with reducing agents are better sensitizers thanconventional sulfur and gold sensitizers.

EXAMPLE 9 Synergistic effect of reducing agent with non-labile seleniumcompound Portion of an emulsion similar to that of Example 1 aresensitized with various sensitizers as set forth below. These emulsionsare then coated and processed in the same manner as in Example 1 withthe following results:

Reducing Relative Portion sensltizer agent speed Gamma Fog First None 301 0.80 0.03 Second Selenous acid (3.27) (non- 30 24 0.37 0. 03

labile selenium compound).

Third Sodium sulfite (6.3) (re- 30 1 0. 12 0.03

ducing agent). Fourth Pzgagfium chloroaurate 25 24 0.28 0.08 FifthSelehoirs acid (3.27 so 25 0.22 0.09

Flogassium chloroaurate Sixth Sodium suifite (6.3) a0 12 0.22 0.13fiOSdSSil-lfll chloroaurate 30 12 0. 22 0. 13 Seventh. Selenous acid(3.27) 10 250 1. 42 0.18

Sodium sultite (6.3). Eighth Selenous acid (3.27) 80- 25 1,000 1.68 0.20

EXAMPLE 7 Effect of reducing agents on labile selenium compounds diumsulfite (6.3) Potassium chloroaurate (1.0)

A first portion of the emulsion of Example 1 is chemi- This exampleshows that activating a non-labile selenium compound with a reducingagent will increase the relative speed of an emulsion by over l000%.'This example also shows that the addition of a gold compound plus areducing agent to a non-labile selenium compound will increase therelative speed of an emulsion by over 4000%.

EXAMPLE 10 A first portion of an emulsion similar to that of Example 1is chemically sensitized with 4 mg. of potassium chloroaurate per silvermole, 100 mg. of sodium thiocyanate per silver mole, 1.6 mg. ofpotassium selenocynate per silver mole and 20.2 mg of benzothiazolemethiodide This example shows that reducing agents have no effect persilver mole and is then heated for 15 minutes at on selenium compoundswhich are already labile (N,N- 65 C.

A second portion of the emulsion is chemically sensitized in the samemanner as the first portion but with the addition of 4 mg. of sodiumthiosulfate per silver mole and heating for minutes at 60 C.

Relative Portion Sensitizer speed Fog First None 1, 000 0.17 Second"...Sodi mthiosuliate 970 0.03

This example shows that sulfur compounds, such as sodium thiosulfate,act as stabilizers in reducing the fog of emulsions sensitized with goldand activated non-labile selenium compounds.

EXAMPLE 11 except that 50 grams per silver mole of a naturally activegelatin was utilized.

These portions of the emulsion are then coated and processed in the samemanner as in Example 1 with the following results:

Relative Portion Gelatin speed Fog First Inert 100 0.16 Second Active118 0. 22

This example illustrates the unpredictability connected with usingpotassium selenocyanate in combination with noble metals as a sensitizerwith various gelatins. U.S. Patent 3,243,298, column 68, lines 35-38,and British Patent 861,984, page 2, lines 42-44 disclose the use ofpotassium selenocyanate as a sensitizer. There is no disclosure of theuse of this compound in combination with noble metals, however, or thatactivation of this compound will give synergistic sensitizing results incombination with noble metals. The limited disclosure in these referenceshould thus be qualified as being dependent upon the type of gelatinemployed. By employing the process of my invention, 1 can obtainreproducible results which are not dependent upon the particular type ofgelatin employed.

7 EXAMPLE 12 Test for labile and non-labile selenium compounds To 10 m1.of distilled water in a test tube is added 6 mg. of potassiumselenocyanate. To this solution approximately 15 ml. of 0.1 N silvernitrate is added. No silver selenide is formed which indicates thatpotassium senelocyanate is a non-labile selenium compound.

To 10 ml. of distilled water in a test tube is added 6 mg. of potassiumselenocyanate. To this solution is added 50 mg. of sodium sulfite. Noreaction occurs. To this solution approximately 5 ml. of 0.1 N silvernitrate is added. A black'precipitate (silver selenide) immediatelyforms. This indicates that the potassium selenocyanate becomes labile inthe presence of sodium sulfite, a reducing agent.

In one embodiment of the present invention we employ a complex formed bygold salt with phosphine. This complex is not itself a sensitizer but itis added as a source of both gold salt as a sensitizer and phosphine asan activator for the non-labile selenium added separately.Triphenylphosphinegold (I) chloride is a well defined complex which hasbeen isolated and purified. See Journ. Chem. Soc., 5751 (1965). Whenadded to the emulsion the complex dissociates liberating the gold saltand triphenylphosphine components.

EXAMPLE 13 Lack of sensitizing ability of the complex by itself; lack ofsensitizing ability of non-labile selenium by itself.

A medium grained silver bromoiodide emulsion containing 3.4 percentiodide was chemically sensitized with (per mole of silver halide) 4.75mg. triphenylphosphinegold (I) chloride and mg. sodium thiocyanate.

A second portion of the emulsion was sensitized with 100 mg. sodiumthiocyanate and 1.4 mg. potassium selenocyanate.

A third portion was sensitized with 4 mg. potassium chloroaurate(equimolar amount of gold, compared to sample 1) and 100 mg. sodiumthiocyanate.

Each of the three samples was heated for 40 minutes at 65 C.

These emulsion samples were then coated on a cellulose acetate supportat a coverage of 540 mg. silver per square foot. The coatings wereexposed on an intensity scale sensitometer, processed for 5 minutes inKodak Developer DK-SO, fixed, washed, and dried.

EXAMPLE 14 Activation of a non-labile selenium compound with thecomplex; simultaneous activation of the gold compound to produce agold-sensitization The emulsion of example 13 was chemically sensitizedwith (per mole of silver) 4.75 mg. triphenylphosphinegold (I) chloride,100 mg. sodium thiocyanate, and 1.4 mg. potassium selenocynate. Thsample was heated for 40 minutes at 65 C.

A second portion of the emulsion was sensitized with 4 mg. potassiumchloroaurate (equimolar to the amount of gold in portion 1), 100 mg.sodium thiocyanate, and 1.4 mg. potassium selenocyanate. The sample washeated for 40 minutes at 65 C.

A third portion of the emulsion was sensitized with 100 mg. sodiumthiocyanate, 1.4 mg. potassium selenocyanate and 2.55 mg.triphenylphosphine (equimolar to the amount of phosphine in the complexof sample 1). This portion was heated 1 minute at 65.

These emulsion samples were coated, exposed, and processed as in Example13.

Relative Portion (description) speed Fog First (phosphine-goldcomplex-l-KSeON) 151 0. 12 Seoon (gold sensit1zer+KSeCN) 100 0. 07 Third(phosphine-i-KSeCN) r 74 0. 13

EXAMPLE 15 Inability of the complex to chemically sensitize with labileselenium The emulsion of Example 13 was chemically sensitized with (permole of silver) 4 mg. of potassium chloroaurate, 100-mg. sodiumthiocyanate, and 1.45 mg. N,N-dimethylselenourea. The portion was heatedfor 5 minutes at 65 C.

A second portion was sensitized with 4.75 mg. triphenyl- 13phosphine-gold (I) chloride, (equimolar in gold to the gold-sensitizerused in sample 1), 100 mg. sodium thiocyanate, and 1.45 mg.N,N-dimethylselenourea. This sample was heated for 20 minutes at 65 C.

The samples were coated, exposed, and processed as in Example 1.

A coarse grained silver bromoiodide emulsion containing 6 mole percentiodide was chemically sensitized with (per mole of silver 2 mg.potassium chloraurate, 50 mg. sodium thiocyanate, 4 mg. sodiumthiosulfate pentahydrate, and 0.5 mg. N,N-dimethylselenourea. The samplewas heated for 5 minutes at 65 C.

A second portion was sensitized with 7.8 mg. triphenylphosphine-goldfl)chloride, 100 mg. sodium thiocyanate and 2.06 mg. Complex D. The samplewas heated for 25 minutes at 65 C.

A third portion of the emulsion was chemically sensitized with 7.8 mg.triphenylphosphine-gold(I) chloride, 100 mg. sodium thiocyanate and 1.8mg. potassium selenocyanate. The sample was heated 20 minutes at 65 C.

The emulsion samples were then coated on a cellulose acetate support ata coverage of 540 mg. silver per square foot. The coatings were exposedon an intensity scale sensitometer, processed for 4 minutes in KodakDeveloper D-19, fixed, washed, and dried.

Relative Portion (description) speed Fog First (Optimum gold-Hablleselenium finish for this emulsion) 100 0.08 Second (gold-phosphinecomplex+isoselenocyanate complex) 1 105 0. Third (gold-phosphinecomplex+KSeGN) 95 0.08

Although the invention has been described in detail with reference tocertain preferred embodiments thereof, variations and modifications canbe effected within the spirit and scope of the invention as describedhereinbefore and as defined in the appended claims.

I claim:

1. A process comprising sensitizing a photographic silver halideemulsion with a sensitizing amount of a noble metal and labile selenium,said labile selenium being formed in situ by activating a non-labileselenium compound.

2. The process of claim :1 wherein said non-labile selenium compound isactivated by a reducing agent.

3. The process of claim 1 wherein said noble metal is gold.

4. The [process of claim 2 wherein said noble metal is gold.

5. The process of claim 1 wherein said non-labile selenium compound iseither potassium selenocyanate or selenous acid.

6. The process of claim 3 wherein said non-labile selenium compound iseither potassium selenocyanate or selenous acid.

7. The process of claim'4 wherein said non-labile selenium compound ispotassium selenocyanate or selenous acid.

8. The process of claim 2 wherein said reducing agent is abenzothiazolium salt, 2-mercaptobenzoic acid, triphenylphosphine,stannous chloride or an alkali metal sulfite.

9. The process of claim 4 wherein said reducing agent is abenzothiazolium salt, Z-mercaptobenzoic acid, triphenylphosphine,stannous chloride or an alkali metal sulfite.

10. The process of claim 7 wherein said reducing agent is abenzothiazolium salt, 2-mercaptobenzoic acid, triphenylphosphine,stannous chloride or an alkali metal sulfite.

11. The process of claim 1 wherein said sensitizing is carried out inthe presence of a water-soluble thiocyanate compound.

12. The process of claim 4 wherein said sensitizing is carried out inthe presence of a water-soluble thiocyanate compound.

13. The process of claim 1 wherein said silver halide emulsion isstabilized with a labile sulfur compound.

14. The process of claim 4 wherein said silver halide emulsion isstabilized with a labile sulfur compound.

15. The process of claim 11 wherein said silver halide emulsion isstabilized with a labile sulfur compound.

References Cited UNITED STATES PATENTS 3,297,446 1/1967 Dunn 961073,297,447 1/ 1967 McVeigh 96107 X NORMAN G. TORCHIN, Primary Examiner.RICHARD E. FICHTER, Assistant Examiner.

